In general, insulated electrically heated pots have a structure provided with a container having a double-walled structure in which an inner container and an outer container are joined and made unitary at the openings thereof, the space between the inner and outer containers being placed in a vacuum state; and a heater unit for heating the liquid stored within the inner container by means of heat transfer.
FIG. 2 shows, as an example of a conventional pot for boiling water, the pot described in Japanese Utility Model, First Publication, No. Sho 62-73836; this water boiling pot 1 has a structure in which a heater unit 3 is affixed to the inner bottom surface of a container 2 having a vacuum double-walled structure in a water-tight manner by means of packings 4 and 5.
However, the conventional vacuum insulated water boiling pot shown in FIG. 2 above has a structure in which the space between the inner container and the outer container is placed in a vacuum state, so that atmospheric pressure is constantly placed on the double-walled container, and in order to disperse this force, a form having curved surfaces is necessary, and as a result, it is generally necessary to provide an inner container and an outer container with a cylindrical form having a bottom, and as a result of employing such a form, there is a problem in that the proportion of the inner capacity with respect to the outer capacity of the outer container, that is to say, the capacity efficiency, is low.